This invention relates to a fabric graft for use with dialysis treatment of blood in general, and more particularly to a high profile graft for arteriovenous access during dialysis treatment.
A healthy kidney removes toxic wastes and excess water from the blood. With partial or chronic renal disease, however, the kidneys progressively stop performing these essential functions. Dialysis treatment is often required to remove toxins and excess water from the blood of a patient.
Hemodialysis therapy is an extracorporeal process which removes toxins and water from a patient""s blood. A hemodialysis machine pumps blood from the patient, through a dialyzer, and then back to the patient. The dialyzer removes the toxins and water from the blood by a membrane diffusion principle. Typically, a patient with chronic kidney disease requires hemodialysis three times per week for 3-6 hours per session. Removing blood from the body requires a vascular access to the patient""s blood system. This vascular access can be accomplished by surgically modifying the patient""s own blood vessels or attaching an artificial device to the blood vessels. If the vascular access site is entirely beneath the skin, the skin and the vascular site is punctured by a needle for access.
Arteriovenous (AV) shunts have been used in the past to provide vascular access. The AV shunt employs a tube sutured to an artery. The tube is tunneled subcutaneously and exited through the skin where it connects to another tube. This second tube penetrates back through the skin and is sutured to a vein. During hemodialysis, the arterial tube connects to an input line of a dialysis machine, and the venous tube connects to the machine""s return line.
Because a portion of the tube remains outside the skin, patients typically suffer a relatively high rate of infection. Other problems associated with the AV shunt include skin disfigurement and frequent clotting.
Problems associated with these transcutaneous shunts led to the development of a native arteriovenous (AV) fistula which remains subcutaneous post-surgery and avoids to some extent the infection problem associated with transcutaneous devices. The AV fistula is a surgical construct subcutaneously connecting a patient""s major artery to a major vein at a convenient location, such as in the arm. With this resulting new blood flow path, most blood will bypass the high flow resistance of the downstream capillary bed, thereby producing a dramatic increase in the blood flow rate through the fistula. Two fistula needles, connected to tubing leading to and from the hemodialysis machine, are used to puncture the skin to gain access to the arterialized vein. Blood is withdrawn from the arterial side of the vein, passes through the dialysis machine, where it is cleansed, and returns to the venous side of the access.
The AV fistula, however, requires four to eight weeks to mature and cannot be used for dialysis access during this time period. The AV fistula matures by thickening of the fistula vein due to increased arterial pressure and arterial flow thereat. After the fistula vein matures or arterializes it becomes feasible to repeatedly puncture the AV fistula vein. The arterialized vein can then be punctured repeatedly, and the high blood flow permits hemodialysis treatment thereat. The AV fistula technique, however, cannot be used on many dialysis patients because the patients who are elderly, diabetic or suffer from arterial disease generally lack usable peripheral veins.
AV grafts made from synthetic materials, such as polytetrafluoroethylene (PTFE), polyurethane or silicone, have been used as alternatives to arteriovenous shunts and fistulas. Implanted in a surgical procedure, the AV graft connects an artery to a vein, forming a bypass which can be punctured by needle sets in the same way a normal AV fistula is accessed.
The AV grafts are commonly used when the patient""s own blood vessels are too small for fistula construction. These grafts, however, typically require about two to four weeks for adequate healing and sufficient tissue growth to stabilize the graft. During this time period the AV graft is generally unavailable for dialysis access.
An AV graft made from conventional PTFE or ePTFE extruded tubes have the disadvantage in that the graft is typically not self-sealing after puncture by a dialysis needle. Digital pressure is often applied near the puncture site for several minutes to prevent bleeding through the puncture site. A polyurethane graft is known to be somewhat unstable in the body. A silicone material generally has greater flexibility than a PTFE material. An AV graft made from silicone has better self-sealing characteristics as compared to an AV graft made from PTFE because of the increased flexibility of the silicone material. Such silicone AV grafts, however, are often stiff and uncomfortable as compared to an AV graft made from PTFE.
There is a need for a self-sealing AV graft that does not have the disadvantages of the ePTFE, polyurethane or silicone AV grafts. In particular, there is a need for a self-sealing AV graft that does not require extended periods of time for healing and tissue growth prior to use in hemodialysis.
The present invention is an AV graft made from synthetic fibers or yarns and having a high external profile to facilitate tissue ingrowth and to provide self-sealing of the graft after puncture by a dialysis needle, or the like. The AV graft includes elastic synthetic fibers to provide a self-sealing mechanism after puncture.
The AV graft of the present invention includes a woven or knitted pattern of yarns. The woven or knitted pattern provides for self-sealing after puncture. The AV graft has a high external profile to promote tissue ingrowth after implantation and to further provide self-sealing of the graft after puncture.
In one aspect the high profile AV graft is a woven graft having a first fabric layer of a plain or twill pattern to provide a smooth interior surface of the graft. A second fabric layer having raised loops is provided to give the AV graft a high external profile. The second fabric layer has raised loops of fabric extending outwardly from the outer surface to provide a raised or velour texture.
In a another aspect, the present invention includes a knitted pattern of yarns. A first fabric layer is provided with a close-knit pattern having a smooth inner surface. A second knit pattern of a second fabric layer has external loops that can be raised from the surface to provide a velour-like surface.
The fabric loops extending from the outer surface of the AV graft extends from about 1 to about 5 mm in length.